FIX: The PostgreSQL service not starting after installation (WSL2 context)

[Arkshine]

In the WSL 2 context installation, for some reason, the service is not starting automatically after the apt installation.
It happens on a fresh Ubuntu 22 installation.

createuser: error: connection to server on socket "/var/run/postgresql/.s.PGSQL.5432" failed: No such file or directory
        Is the server running locally and accepting connections on that socket?
failed

The proposed & tested solution is to check if the service is up; if not, we start it.
service postgresql status returns a non-zero exit code if the service isn’t running.

[timhaines]

This is needed for Ubuntu 18 too, and probably Ubuntu 20.